When the Wrights began their studies of aviation, they did not overlook the great experts on the subject—the birds. In his letter to the Smithsonian, Wilbur wrote that birds “are the most perfectly trained gymnasts in the world and are specially well fitted for their work, and it may be that man will never equal them.”

Wilbur became particularly interested in the turkey vulture, or buzzard. In a letter to aviation experimenter Octave Chanute, he noted that when one wing tip is twisted upward and the other downward, the buzzard “becomes an animated windmill and instantly begins to turn.”

The brothers began to think about mechanisms that would similarly “warp” the wings of a flying machine and allow the pilot to maintain lateral balance and to make lateral turns. Wilbur happened upon an idea one day at the bicycle shop. While talking to a customer, he idly picked up a cardboard container for a bicycle inner tube, which was empty and open at both ends. Holding the rectangular box in both hands, he pressed down on opposite corners. The other two corners moved simultaneously—one went up and the other went down—but the box otherwise retained its shape. Imagining the box as a span of wings, he saw that wing tips could be simultaneously warped, perhaps by a system of wires.

In the summer of 1899, the Wrights designed such a system for a biplane kite. When they were satisfied that the system could be applied to a “man-carrying” glider, they traveled to Kitty Hawk, North Carolina, to test the glider.